1. Field of the Invention
The present invention relates to train parking brake systems and, more particularly, to a system and method for controlling a rail car braking system.
2. Description of the Related Art
Parking brake systems for railway are well-known and generally use a mechanical source of parking brake force that is held off by air pressure. One embodiment in particular is the spring applied/air released parking brake, which uses a large spring for the parking force. The spring is normally held in the compressed state and allowed to expand to apply the parking brake. The parking brake is then released when the system is pressurized to recompress the spring.
Another conventional parking brake system is the Parkloc® system available from New York Air Brake, LLC of Watertown, N.Y., which is additionally described in U.S. Pat. Nos. 7,163,090 and 7,377,370. The Parkloc® system uses a pneumatically controlled, mechanical locking mechanism to lock the air brake cylinder in the applied, loaded state. As a result, even if the air brake cylinder subsequently leaks away due to a long parking duration, the brakes are mechanically held in the applied position. The latching mechanism in the Parkloc is piloted by brake pipe pressure and is arranged to lock when brake pipe pressure drops below 60 psi and unlock when brake pipe exceeds 65 psi. Although the actual pressures to lock and unlock can be defined by the design of the latching piston, including the piston area and spring preloads, the hysteresis, i.e., the difference between locking and unlocking pressures, is not so easily changed, as locking and unlocking are the result of pressurizing a single piston element with a fixed wetted area.
In normal operation, it is not uncommon for a train to be forced to stop on a grade. Because the AAR brake systems used on freight trains are a direct release system, recharge of the air brake system is done simultaneously with brake system release. To prevent the train from rolling away on a grade during this release and recharge process, the train crew manually sets the handbrakes on a sufficient number of the cars in the train to hold the train stationary. Once the hand brakes are set, the train air brakes are released and recharged. The hand brakes must then be manually released before the train can be moved.
While a Parkloc® parking brake system would hold a train on a grade in a parked state with the brake pipe vented, as soon as the brake pipe pressure exceeded the release pressure, e.g., 65 psi, the parking brake will release simultaneously with the air brakes. As a result, it is desired to have a parking brake system which will not release until the train brakes are substantively recharged and which can be controlled from by the driver of the locomotive without the need for someone to walk the length of the train to manually release the hand brakes that were set on a sufficient number of the cars in the train to hold the train in stationary position.